Brain Freeze: Pembrolizumab-Induced Autoimmune Encephalitis in Triple-Negative Breast Cancer.

This case report presents the first known instance of pembrolizumab-induced autoimmune encephalitis in a 41-year-old female patient with stage IIIc triple-negative breast cancer. The patient developed expressive aphasia three days after starting pembrolizumab in combination with chemotherapy, prompting comprehensive evaluations that ruled out infectious or metastatic causes. A diagnosis of pembrolizumab-associated autoimmune encephalitis was established following a lumbar puncture and MRI. After discontinuing the immune checkpoint inhibitors (ICI) and initiating high-dose corticosteroids (methylprednisolone), the patient's symptoms significantly improved within days. This case highlights the importance of recognizing and managing neurological immune-related adverse events (irAEs) associated with ICIs, as their incidence can be variable but potentially severe. Clinicians must maintain a high index of suspicion for neurological irAEs, especially with new neurological symptoms, as early diagnosis and intervention are crucial for optimizing patient outcomes while balancing effective cancer treatment. Ongoing research is essential to elucidate the mechanisms and management strategies for ICI-related autoimmune encephalitis.